The present invention relates to a plasma processing apparatus and a plasma processing method.
An etching apparatus is utilized in a process for manufacturing semiconductor devices in the prior art. The etching apparatus employed in the manufacturing process is often a plasma etching apparatus constituted by providing an upper electrode and a lower electrode facing opposite each other within a processing chamber. In such an etching apparatus, the processing gas introduced into the processing chamber is raised to plasma when high-frequency power is applied to the lower electrode. In the plasma etching apparatus structured as described above, a workpiece placed on the lower electrode, e.g., a semiconductor wafer (hereafter referred to as a xe2x80x9cwaferxe2x80x9d), undergoes a plasma etching process.
In addition, a wafer having undergone the process is taken out of the processing chamber in the following manner. First, while sustaining the atmosphere inside the processing chamber at a reduced pressure which is required for the process, the lower electrode is lowered from the plasma processing position near the upper electrode to the wafer delivery position located further downward. Also, the application of the high level DC voltage to the electrostatic chuck vacuum holding the wafer is stopped. Next, when the lower electrode is completely lowered to the delivery position, a lifter pin is raised to remove the wafer from the mounting surface and position it above the mounting surface. Then, a gate valve connecting the processing chamber and a delivery chamber is released to carry the wafer from the processing chamber into the delivery chamber.
The electrostatic chuck is constituted by enclosing a conductive thin film with an insulating thin film. Consequently, the wafer placed on the electrostatic chuck is insulated from the ground. If plasma processing is performed in this state, the electrical charge accumulated at the wafer is not released due to the presence of the electrostatic chuck even after the processing is completed, and thus, the electrical charge remains at the wafer as a residual charge. In addition, the wafer is transported after the lower electrode is lowered to the delivery position in the apparatus described above. As a result, the distance between the wafer on the lower electrode and the upper electrode increases as the lower electrode travels downward. The voltage between the wafer and the upper electrode attributable to the residual charge increases as the distance between the wafer and the upper electrode lengthens. For instance, if the distance between the wafer set at the delivery position and the upper electrode is four times as large as the distance between the wafer set at the plasma processing position and the upper electrode, the voltage between the wafer set at the delivery position and the upper electrode becomes as high as five times the voltage between the wafer set at the plasma processing position and the upper electrode, as calculated by using the following formula:
V=(Qxc2x7d)/(Sxc2x7xcex5).
It is to be noted that in the expression above, V represents the voltage between the wafer and the upper electrode, Q represents the residual charge at the wafer, d represents the distance between the wafer and the upper electrode, S represents the surface area of the wafer and xcex5 represents the dielectric constant. Thus, when the gas inside the delivery chamber is allowed to flow into the processing chamber by releasing the gate valve, a local discharge occurs between the wafer and the conductive lifter pin, to cause damage to the wafer. This problem also occurs when the internal wall of the processing chamber facing opposite the mounting surface of the lower electrode is constituted of a dielectric material, as in a microwave type plasma etching apparatus or an inductively-coupled plasma etching apparatus.
There is a technology in the prior art that has been proposed to prevent the abnormal discharge described above by introducing an inert gas into the processing chamber before lowering the lower electrode to the delivery position and thus causing the residual charge at the wafer to self discharge. However, there is a problem in that it is difficult to introduce a large volume of the inert gas in a short period of time by introducing the inert gas from a processing gas supply system, resulting in a reduction in throughput. Furthermore, another gas supply system must be provided in order to introduce the inert gas from a dedicated gas supply system. This necessitates a major modification of the apparatus structure leading to an increase in the initial cost.
An object of the present invention, which has been completed by addressing the problems of the prior art discussed above, is to provide a new and improved plasma processing apparatus and a new and improved plasma processing method that make it possible to eliminate the problems described above and other problems.
In order to achieve the object described above, in a first aspect of the present invention, a plasma processing apparatus for implementing a plasma processing on a workpiece, comprising plasma processing chamber, the atmosphere in which is sustained at a reduced pressure during the plasma processing, an electrode provided inside the plasma processing chamber that is constituted to allow the workpiece to be placed thereupon and is capable of traveling between an upper plasma processing position and a lower delivery position, an electrostatic chuck provided at a mounting surface of the electrode that detachably electrostatic holds the workpiece when a high level DC voltage is applied thereto, a delivery chamber engaged in transfer of the workpiece with the plasma processing chamber with the atmosphere therein sustained at a higher pressure compared to the atmosphere in the plasma processing chamber, a means for opening/closing which connects/disconnects the plasma processing chamber and the delivery chamber while retaining the airtightness therein and a means for control that engages in control to introduce a gas inside the delivery chamber into the plasma processing chamber by opening the means for opening/closing until the electrode departing the plasma processing position reaches the delivery position after the plasma processing is completed, is provided, as disclosed in claim 1.
According to the present invention, the high-pressure gas inside the delivery chamber can be introduced into the plasma processing chamber by opening the means for opening/closing before the electrode completes its descent to the delivery position following the end of plasma processing. Thus, in a plane-parallel type plasma processing apparatus, for instance, the residual charge at the workpiece can be eliminated by causing the residual charge to become gently released by itself before the voltage between the upper electrode facing opposite the lower electrode and the workpiece becomes high. In addition, in a microwave type plasma processing apparatus or an inductively-coupled plasma processing apparatus, the residual charge at the workpiece can be eliminated in a manner similar to that described above before the voltage between the top plate constituted as a dielectric wall facing opposite the electrode and the workpiece becomes high. As a result, no abnormal discharge occurs even when the workpiece is disengaged from the electrode having completed its descent to the delivery position, to prevent damage to the workpiece. Normally, a gas at a pressure higher than the pressure of the gas inside the plasma processing chamber is constantly introduced into the delivery chamber at a high flow rate in order to prevent particles inside the plasma processing chamber from circulating while the means for opening/closing is opened. Furthermore, the workpiece intake/outlet communicating between the space inside the plasma processing chamber and the space inside the delivery chamber is formed over a relatively large range to allow a means for delivery holding the workpiece to pass through. Thus, the gas can be instantaneously introduced into the plasma processing chamber without having to make a major design modification in the apparatus structure. Consequently, the speed at which the electrode travels while introducing the gas does not need to be lowered and a reduction in throughput is prevented. Moreover, the present invention can be implemented with ease while minimizing an increase in the initial cost.
In addition, as disclosed in claim 2, for instance, the means for control should engage in control for applying a high level DC voltage to the electrostatic chuck having the reverse polarity from the polarity of the high level DC voltage applied to the electrostatic chuck while the electrostatic chuck is vacuum holding the workpiece, until immediately after the means for opening/closing is opened. In this structure, by applying the high level DC voltage with the reverse polarity, the self discharge of the residual charge at the workpiece can be introduced with further ease. As a result, the residual charge is minimized. Thus, the workpiece can be disengaged from the electrostatic chuck with ease to prevent a generation of particles. Furthermore, occurrence of an abnormal discharge at the workpiece can be prevented with a high degree of reliability.
In a second aspect of the present invention, a plasma processing method for implementing plasma processing on a workpiece in a reduced pressure atmosphere by placing the workpiece at a mounting surface of an electrode provided inside a plasma processing chamber and applying a high level DC voltage to an electrostatic chuck provided at the mounting surface of the electrode to cause the electrostatic chuck to vacuum hold the workpiece, comprising a step in which the electrode is moved from an upper plasma processing position to a lower delivery position after the plasma processing ends and a step in which a means for opening/closing that switchably connects a delivery chamber engaged in transfer of the workpiece to/from plasma processing chamber, with the plasma processing chamber, is opened before the electrode reaches the delivery position and the gas inside the delivery chamber the atmosphere, which is sustained at a higher pressure than the atmosphere inside the plasma processing chamber, is introduced into the plasma processing chamber, as disclosed in claim 12, is provided.
According to the present invention, the pressure inside the plasma processing chamber is raised by introducing the high-pressure gas inside the delivery chamber into the plasma processing chamber before the electrode reaches the delivery position following the plasma processing end. As a result, the residual charge at the workpiece can be eliminated before the pressure between the workpiece and the upper electrode or between the workpiece and the dielectric wall becomes high, to prevent damage to the workpiece.
In addition, it is desirable for the plasma processing method to further comprise a step in which a high level DC voltage with a reverse polarity from the polarity of the high level DC voltage applied to the electrostatic chuck while the electrostatic chuck is vacuum holding the workpiece is applied to the electrostatic chuck until immediately after the means for opening/closing is opened, as in the invention disclosed in claim 13, for instance. Through this method, the self discharge of the residual charge at the workpiece is further promoted.